Incident ray always lies in a plane

Options

A. perpendicular to plane containing normal and reflected ray
B. perpendicular to normal
C. perpendicular to plane containing reflected ray
D. containing reflected ray and normal

Answer

To solve the question "Incident ray always lies in a plane," we will analyze the relationship between the incident ray, the reflected ray, and the normal line at the point of incidence on a reflective surface (like a mirror).

### Step-by-Step Solution:

1. **Understanding the Setup**:
- Consider a flat mirror. When light strikes the mirror, it creates an incident ray that approaches the surface.
- At the point where the incident ray meets the mirror, we can draw a line called the normal, which is perpendicular to the surface of the mirror.

2. **Identifying the Rays**:
- The incident ray is the ray of light that strikes the mirror.
- The reflected ray is the ray of light that bounces off the mirror after striking it.
- The normal line is the line perpendicular to the mirror at the point of incidence.

3. **Analyzing the Plane**:
- The incident ray, the reflected ray, and the normal all lie in the same geometric plane. This means that if you were to draw a flat surface through these three lines, they would all be contained within that surface.
- This is a fundamental principle of reflection in optics.

4. **Evaluating the Options**:
- **Option 1**: Perpendicular to the plane containing the normal and the reflected ray - **Incorrect**. The incident ray is not perpendicular to this plane.
- **Option 2**: Perpendicular to the normal - **Incorrect**. The incident ray is not perpendicular to the normal; it makes an angle with it.
- **Option 3**: Perpendicular to the plane containing the reflected ray - **Incorrect**. The incident ray is not perpendicular to the plane of the reflected ray.
- **Option 4**: Perpendicular to the plane containing the reflected ray and normal - **Correct**. The incident ray, reflected ray, and normal all lie in the same plane.

5. **Conclusion**:
- Therefore, the correct answer is that the incident ray always lies in the same plane as the normal and the reflected ray.

### Final Answer:
**The correct option is 4: The incident ray lies in the same plane as the normal and the reflected ray.**